CT detector array having non-pixelated scintillator array

ABSTRACT

The present invention is a directed to a non-pixelated scintillator array for a CT detector as well as an apparatus and method of manufacturing same. The scintillator array is comprised of a number of ceramic fibers or single crystal fibers that are aligned in parallel with respect to one another. As a result, the pack has very high dose efficiency. Furthermore, each fiber is designed to direct light out to a photodiode with very low scattering loss. The fiber size (cross-sectional diameter) may be controlled such that smaller fibers may be fabricated for higher resolution applications. Moreover, because the fiber size can be controlled to be consistent throughout the scintillator array and the fibers are aligned in parallel with one another, the scintillator array, as a whole, also is uniform. Therefore, precise alignment with the photodiode array or the collimator assembly is not necessary.

The present application is a divisional and claims priority of U.S.patent application Ser. No. 10/249,694 filed Apr. 30, 2003, now U.S.Pat. No. 7,054,408 B2, the disclosure of which is incorporated herein.

BACKGROUND OF INVENTION

The present invention relates generally to diagnostic imaging and, moreparticularly, to a non-pixelated scintillator array incorporated into adetector array for a CT imaging system. More particularly, the inventionrelates to a scintillator array formed of a plurality of ceramic orsingle crystal fibers as well as a method and apparatus for forming theceramic or single crystal scintillator fibers.

Typically, in computed tomography (CT) imaging systems, an x-ray sourceemits a fan-shaped beam toward a subject or object, such as a patient ora piece of luggage. Hereinafter, the terms “subject” and “object” shallinclude anything capable of being imaged. The beam, after beingattenuated by the subject, impinges upon an array of radiationdetectors. The intensity of the attenuated beam radiation received atthe detector array is typically dependent upon the attenuation of thex-ray beam by the subject. Each detector element of the detector arrayproduces a separate electrical signal indicative of the attenuated beamreceived by each detector element. The electrical signals aretransmitted to a data processing system for analysis which ultimatelyproduces an image.

Generally, the x-ray source and the detector array are rotated about thegantry within an imaging plane and around the subject. X-ray sourcestypically include x-ray tubes, which emit the x-ray beam at a focalpoint. X-ray detectors typically include a collimator for collimatingx-ray beams received at the detector, a scintillator for convertingx-rays to light energy adjacent the collimator, and photodiodes forreceiving the light energy from the adjacent scintillator and producingelectrical signals therefrom.

Typically, each scintillator of a scintillator array converts x-rays tolight energy. Each scintillator illuminates and thereby discharges lightenergy to a photodiode adjacent thereto. Each photodiode detects thelight energy and generates a corresponding electrical signal. Theoutputs of the photodiodes are then transmitted to the data processingsystem for image reconstruction.

Each photodiode of the photodiode array is aligned to correspond with ascintillator of the scintillator array. Known CT detectors havepixelated scintillator arrays that, ideally, are dimensionallyequivalent throughout the scintillator array. Because there is aone-to-one relationship between photodiode and scintillator, it isimperative that each scintillator be precisely aligned with eachphotodiode. This precision becomes increasingly important as a result ofthe exactness required when developing reflector elements between thescintillator pixels and coupling a single-piece or multi-piececollimator assembly to the scintillator array. Because it is extremelydifficult to form a small channel or groove between each pixelatedstructure, thicker reflector plates or walls are used to separate eachof the scintillators. This leads to decreased surface area of the activescintillator and reduced quantum detection efficiency or dose usage.Reflector protecting material, such as tungsten, absorbs x-rays therebyincreasing the radiation dosage required for data acquisition.Additionally, the specification for misalignment is usually very limitedto maintain acceptable image quality. Further, high resolutionapplications require small scintillation cells which are difficult toform into a pixelated layout.

A number of fabrication techniques have been developed to achieve thenecessary precision. These techniques include developing a ceramic waferusing well-known semiconductor fabrication processes and, throughprecisely controlled dicing and grinding, forming scintillator arrays orpacks. Using accurate dicing and grinding processing and equipment, thepacks may be processed to develop a series of pixelated structures. Asnoted above, however, the pixelated structures must be exactly alignedso that misalignment between the scintillators, photodiodes, and thecollimator assembly during subsequent fabrication is minimized.Misalignment, however minor, can contribute to cross-talk, x-raygenerated noise, and radiation damage to the photodiode array. If themisalignment is too severe, the scintillator pack must be discardedthereby increasing fabrication costs, labor, time, and waste.

Therefore, it would be desirable to design an apparatus and method offabricating a scintillator array for high resolution CT imaging withreduced sensitivities to alignment of the scintillator array with thephotodiode array and/or collimator assembly.

BRIEF DESCRIPTION OF INVENTION

The present invention is a directed to non-pixelated scintillator arrayfor a CT detector as well as an apparatus and method of manufacturingsame that overcomes the aforementioned drawbacks. The scintillator arrayis comprised of a number of ceramic or single crystal fibers that arealigned in parallel with respect to one another. The fibers may haveuniform or non-uniform cross-sectional diameters. The fibers arearranged in a scintillator array or pack that has relatively littlereflector material disposed between adjacent fibers. As a result, thepack has very high dose efficiency. Furthermore, each fiber is designedto direct light out to a photodiode with very low scattering loss. Inthis regard, the scintillator array has a relatively high light outputbut low cross-talk. The fiber size (cross-sectional diameter) may becontrolled such that smaller fibers may be fabricated for higherresolution applications. Moreover, because the fiber size can becontrolled to be consistent throughout the scintillator array and thefibers are aligned in parallel with one another, the scintillator array,as a whole, also is uniform. Therefore, precise alignment with thephotodiode array or the collimator assembly is not necessary.

Therefore, in accordance with one aspect of the present invention, a CTdetector array includes a plurality of collimator elements configured tocollimate x-rays projected thereat as well as a non-pixelatedscintillator pack formed of a material that illuminates upon receptionof x-rays. The CT detector array further includes a photodiode arrayoptically coupled to the non-pixelated scintillator pack and configuredto detect illumination from the scintillator pack and output electricalsignals responsive thereto.

In accordance with another aspect of the present invention, a CTdetector array comprising a non-pixelated array of scintillationelements configured to illuminate upon the reception of high frequencyelectromagnetic energy and coupled to an array of light detectionelements configured to detect illumination of the array of scintillationelements and output a plurality of electrical signals generallyindicative of high frequency electromagnetic energy received by thearray of scintillation elements is provided. The detector array isformed by developing the plurality of single crystal fibers ofscintillation material and casting the plurality of crystal fibers withan adhesive material. The detector array is further formed by curing theplurality of crystal fibers in adhesive material to form a cured packand cutting the cured pack to a specified dimension.

According to another aspect of the present invention, a method ofmanufacturing a CT detector array having a non-pixelated scintillatorarray includes the steps of developing a material base from whichscintillators may be grown and pulling a rod of scintillating materialfrom a material base. The method further includes cutting the rod toform a plurality of scintillator fibers and aligning the plurality ofscintillator fibers into a scintillator bundle. The scintillator bundleis then sliced into a number of scintillator packs whereupon a reflectorcoating is applied to the number of scintillator packs.

Various other features, objects and advantages of the present inventionwill be made apparent from the following detailed description and thedrawings.

BRIEF DESCRIPTION OF DRAWINGS

The drawings illustrate one preferred embodiment presently contemplatedfor carrying out the invention.

In the drawings:

FIG. 1 is a pictorial view of a CT imaging system.

FIG. 2 is a block schematic diagram of the system illustrated in FIG. 1.

FIG. 3 is a perspective view of one embodiment of a CT system detectorarray.

FIG. 4 is a perspective view of one embodiment of a detector.

FIG. 5 is illustrative of various configurations of the detector in FIG.4 in a four-slice mode.

FIG. 6 is a top view of a scintillator pack in accordance with thepresent invention.

FIG. 7 is a flow chart setting forth the steps of one technique forfabricating the scintillator pack of FIG. 6.

FIG. 8 is a schematic representation of an apparatus capable ofimplementing the technique of FIG. 7.

FIG. 9 is a flow chart setting forth the steps of another technique forfabricating the scintillator pack of FIG. 6.

FIG. 10 is a schematic illustrating one apparatus for carrying out thesteps of FIG. 9.

FIG. 11 is a schematic illustrating another apparatus for carrying outthe steps of FIG. 9.

FIG. 12 is a pictorial view of a CT system for use with a non-invasivepackage inspection system.

DETAILED DESCRIPTION

The operating environment of the present invention is described withrespect to a four-slice computed tomography (CT) system. However, itwill be appreciated by those skilled in the art that the presentinvention is equally applicable for use with single-slice or othermulti-slice configurations. Moreover, the present invention will bedescribed with respect to the detection and conversion of x-rays.However, one skilled in the art will further appreciate that the presentinvention is equally applicable for the detection and conversion ofother high frequency electromagnetic energy. The present invention willbe described with respect to a “third generation” CT scanner, but isequally applicable with other CT systems.

Referring to FIGS. 1 and 2, a computed tomography (CT) imaging system 10is shown as including a gantry 12 representative of a “third generation”CT scanner. Gantry 12 has an x-ray source 14 that projects a beam ofx-rays 16 toward a detector array 18 on the opposite side of the gantry12. Detector array 18 is formed by a plurality of detectors 20 whichtogether sense the projected x-rays that pass through a medical patient22. Each detector 20 produces an electrical signal that represents theintensity of an impinging x-ray beam and hence the attenuated beam as itpasses through the patient 22. During a scan to acquire x-ray projectiondata, gantry 12 and the components mounted thereon rotate about a centerof rotation 24.

Rotation of gantry 12 and the operation of x-ray source 14 are governedby a control mechanism 26 of CT system 10. Control mechanism 26 includesan x-ray controller 28 that provides power and timing signals to anx-ray source 14 and a gantry motor controller 30 that controls therotational speed and position of gantry 12. A data acquisition system(DAS) 32 in control mechanism 26 samples analog data from detectors 20and converts the data to digital signals for subsequent processing. Animage reconstructor 34 receives sampled and digitized x-ray data fromDAS 32 and performs high speed reconstruction. The reconstructed imageis applied as an input to a computer 36 which stores the image in a massstorage device 38.

Computer 36 also receives commands and scanning parameters from anoperator via console 40 that has a keyboard. An associated cathode raytube display 42 allows the operator to observe the reconstructed imageand other data from computer 36. The operator supplied commands andparameters are used by computer 36 to provide control signals andinformation to DAS 32, x-ray controller 28 and gantry motor controller30. In addition, computer 36 operates a table motor controller 44 whichcontrols a motorized table 46 to position patient 22 and gantry 12.Particularly, table 46 moves portions of patient 22 through a gantryopening 48.

As shown in FIGS. 3 and 4, detector array 18 includes a plurality ofsingle scintillator fibers 57 forming a scintillator array 56. Acollimator assembly 59 is positioned above scintillator array 56 tocollimate x-ray beams 16 before such beams impinge upon scintillatorarray 56. In one embodiment, the collimator assembly is integrallyformed with a top or x-ray reception surface of the scintillator array.

In one embodiment, shown in FIG. 3, detector array 18 includes 57detectors 20, each detector 20 having an array size of 16×16. As aresult, array 18 has 16 rows and 912 columns (16×57 detectors) whichallows 16 simultaneous slices of data to be collected with each rotationof gantry 12.

Switch arrays 80 and 82, FIG. 4, are multi-dimensional semiconductorarrays coupled between scintillator array 56 and DAS 32. Switch arrays80 and 82 include a plurality of field effect transistors (FET) (notshown) arranged as multi-dimensional array. The FET array includes anumber of electrical leads connected to each of the respectivephotodiodes 60 and a number of output leads electrically connected toDAS 32 via a flexible electrical interface 84. Particularly, aboutone-half of photodiode outputs are electrically connected to switch 80with the other one-half of photodiode outputs electrically connected toswitch 82. Additionally, a thin reflector layer (not shown) may beinterposed between each scintillator fiber 57 to reduce light scatteringfrom adjacent scintillators. Each detector 20 is secured to a detectorframe 77, FIG. 3, by mounting brackets 79.

Switch arrays 80 and 82 further include a decoder (not shown) thatenables, disables, or combines photodiode outputs in accordance with adesired number of slices and slice resolutions for each slice. Decoder,in one embodiment, is a decoder chip or a FET controller as known in theart. Decoder includes a plurality of output and control lines coupled toswitch arrays 80 and 82 and DAS 32. In one embodiment defined as a 16slice mode, decoder enables switch arrays 80 and 82 so that all rows ofthe photodiode array 52 are activated, resulting in 16 simultaneousslices of data for processing by DAS 32. Of course, many other slicecombinations are possible. For example, decoder may also select fromother slice modes, including one, two, and four-slice modes.

As shown in FIG. 5, by transmitting the appropriate decoderinstructions, switch arrays 80 and 82 can be configured in thefour-slice mode so that the data is collected from four slices of one ormore rows of photodiode array 52. Depending upon the specificconfiguration of switch arrays 80 and 82, various combinations ofphotodiodes 60 can be enabled, disabled, or combined so that the slicethickness may consist of one, two, three, or four rows of scintillatorarray elements 57. Additional examples include, a single slice modeincluding one slice with slices ranging from 1.25 mm thick to 20 mmthick, and a two slice mode including two slices with slices rangingfrom 1.25 mm thick to 10 mm thick. Additional modes beyond thosedescribed are contemplated.

Referring now to FIG. 6, a top view of a scintillator pack constructedin accordance with the present invention is shown. The scintillator pack86 is defined by a plurality of single crystal or ceramic fibers 88 thatdimensionally populate the pack. As will be described in greater detailbelow, a number of techniques may be used to develop fibers 88. Each ofthe scintillator fibers are cylindrical in shape are constructed tofocus light generated upon the reception of x-rays or y-rays toward aphotodiode, as discussed with respect to FIGS. 3-4. In one embodiment,the scintillator fibers have a uniform cross-sectional diameter. Assuch, there is uniformity in scintillator size throughout the pack 86.Some of the advantages of this uniformity will be explained in greaterdetail below. In another embodiment, the fibers may be developed andarranged such that there are differences in cross-sectional diameterwithin the pack. This non-uniformity may be suitable or preferred forsome applications. Moreover, incorporation on non-uniform elements intopack 86 may allow for more fibers to fit within the pack. The morescintillation elements or fibers fit within the pack increases packingefficiency which also improves dose efficiency. That is, increasing thenumber of scintillation cells within a fixed space reduces the amount ofnon-scintillation surface area within the fixed space. Accordingly, themore scintillation material used within the fixed space increases thenumber of x-rays or y-rays detected within that fixed space. As will bedescribed in greater detail below, the present invention allow forformation of smaller scintillation elements or fibers which allows formore scintillator material within a single scintillator pack or array.In further embodiments, the fibers may be grown to have uniformdiameters but non-circular in cross-sectional shape or developed to havenon-uniform diameters and non-circular cross-sections.

That shown in FIG. 6 illustrates a scintillator pack but may alsoillustrate a finished scintillator array. That is, the pack 86 shown inFIG. 6 may be cut or diced to form a scintillator array for a CTdetector cell. In the embodiment having uniformity in fiber sizethroughout the pack, it is not critical that the pack be cut or diced atprecise positions. That is, the entire pack is uniform; therefore, anysection or portion cut away from the pack will also be uniform. As aresult, the uniform packs 86 may be constructed and arbitrarily diced tomatch the dimensional requirements needed for a CT detector or otherdetector assembly. By fabricating uniform packs that may be cut or dicedto form smaller and also uniform portions, a single manufacturingassembly or process may be developed whereupon the appropriately sizedscintillator arrays are cut from the uniform pack rather thanfabricating each of the differing sized arrays or packs separately andindependently. This streamlining and consistency in the scintillatorfabrication process reduces manufacturing costs, tooling, time, labor,and the like.

Still referring to FIG. 6, because each of the scintillator fibers 88may be constructed to have a constant cross-sectional diameter andthereby create a uniformity throughout the scintillator pack 86, thealignment of the collimator assembly and the photodiode array to theresultant scintillator array is less critical. That is, unlike thephotodiode, scintillator arrays developed from pack 86 are notpixilated. The non-pixelated orientation and layout of the scintillatorfibers avoids alignment issues typically associated with the alignmentof the photodiode to the scintillator array. Moreover, alignmentconcerns typically associated with the collimator assembly grid are alsoalleviated.

As stated above, the scintillator fibers may be ceramic fibers or singlecrystal fibers. Ceramic fibers are typically formed using an extrusionmethod with an organic binder. However, the burnout of the binder isusually very difficult and cracks in the structure can occur relativelyeasily. Further, the residue from the organic binder can cause seriousdeterioration of the performance of the scintillator that negativelyaffects light output, radiation damage resistance, and afterglow.Standard extrusion methods utilize an entire powder process whereuponeach of the chemicals used to the form the scintillators are placed inpowder form. However, the powder size greatly affects the density of thescintillator fiber and its sinter-ability. Accordingly, in accordancewith one embodiment of the invention, a fabrication process for singleceramic fibers has been developed that is easy to control, avoids thedrawbacks of separate powdering process typically associated with theextrusion.

Referring now to FIG. 7, a scintillator fabrication process map isshown. With this process or technique, the grain size of the createdceramic fiber is smaller than that typically provided by extrusion whichyields pack density of close to 100 percent. The technique 100 begins at102 with the dissolution of chemicals used to form a precursor solutionat 104. The chemicals selected depend upon the type of scintillatorsystem to be created. For example, in one system, the starting chemicalsinclude lutetium acetate hydrate (>99.99%) (Lu(O₂CCH₃)₃×H₂O), terbiumacetate hydrate (>99.99%) (Tb(O₂CCH₃)₃×H₂O), cerium nitrate (>99.99%)(Ce(NO₃)₃6H₂O), and aluminum formate hydrate (>99.99) (Al(O₂CH)₃3H₂O)with a proper ratio. For example, the proper ratio may be defined by thefollowing stoichiometrical equation, Lu_(0.8)Tb_(2.17)Ce_(0.03)Al₅O₁₂.One skilled in the art would readily recognize that other compositionratios may be possible, such as those discussed in U.S. Ser. No.10/316,151, now U.S. Pat. No. 6,793,848 B2, which is incorporated hereinby reference and conunonly assigned to the Assignee of this application.The starting chemicals are then dissolved in hot distilled water 104 toform the precursor solution. Certain amounts of formic acid, ethyleneglycol, and isobutyric acid are added to stabilize the solution.Alternately, the starting materials or chemicals are all nitrates. Thenitrates are then dissolved in distilled water. Ethylene glycol andacetic acid or citric acid is then added to the dissolved solution.

Once the precursor solution is developed, the solution is heated 106 atabout 60 to 80° C. to dry the water and increase the viscosity bypolymerization. After sufficient drying, the solution becomes atranslucent and, preferably, transparent gel with proper viscosity. Fromthe gel, a precursor fiber is drawn from the gel at 108. The precursorfiber, as will described below, will form the basis for a plurality ofceramic scintillator fibers. The drawn or pulled fiber of gel materialwill be dried 110 in a drying oven at about 100 to 150° C. to dry up thesolvent. The dried fiber will then be pulled into a temperature gradientfurnace for calcining at 112. The first stage in the furnace ispyrolysis at about 400° C. to 1100° C. The fiber will be converted intoa ceramic phase of garnet structure.

Once the ceramic fiber is formed, the fiber will undergo a sinteringstage at 114 with a temperature between 1650 and 1775° C. and,preferably, about 1700° C. for full densification and desired graingrowth. The final stage performed in the furnace is thermal annealing.It should be noted that the pyrolysis, sintering, and annealing stepsmay be done in three separate furnaces for atmospheric control. Thefinal and annealed fiber will then be cut resulting in plurality ofuniformly shaped ceramic scintillator fibers. Generally, the fibers willbe 1-10 μm in size. The fibers are then aligned in a mold at 116. Themold is designed to closely pack and align each of the fibers inparallel with one another. The mold also dimensionally defines theresulting scintillator pack. The bundle of scintillator fibers are thencast with an adhesive material loaded with reflector material 118, suchas titanium oxide (TiO₂). The reflector material is a radiationresistant epoxy with low viscosity. Because the fibers are closelyaligned within the mold, the voids between each fiber are minute. Thesevery small voids, however, are filled with reflector material used toimprove light emissions toward the photodiode array and reduce crosstalk between adjacent scintillator fibers.

Following casting of the fiber bundle with adhesive, the bundle is curedat 120 to form a scintillator pack of reflective coated scintillatorfibers. The cure pack is then sliced at 122 to form a number ofscintillator arrays having uniformly aligned scintillator fibers.Preferably, the pack is sliced along lines perpendicular to the fibers'longitudinal axis. A layer of optically reflective material, such asreflector tape, is then coated on one surface of each scintillator arrayat 124. The surface may also be polished and the sputter coated withreflective material such as aluminum, silver, gold, and the like.Following application of the optically reflective layer, if any, anumber of uniformly sized scintillator arrays or packs result and theprocess ends at 126.

In another embodiment, the starting materials or chemicals used todevelop the precursor solution include Y₂O₃, Gd₂O₃, Eu₂O₃ (all >99.99%),and Pr(NO₃)₃ ⁻×H₂O (>99.99%). With this embodiment, the oxides ofdesired ratio will be mixed together and dissolved in nitric acid. Thenthe praseodymium nitrate will be added into the solution. A certainamount of ethylene glycol and nitric acid will be added to make atransparent solution. The solution will be heated at about 60-80° C. forpolymerization. Once the solution becomes a transparent gel and theviscosity is suitable, a fiber will be drawn from the gel. The rest ofthe fabrication process will be similar to that described above withrespect to the Lu—Tb—Al—O—Ce system, only the temperature and atmospherewill be different. One example of the composition in accordance withthis system is(Y_(1.67)Gd_(0.33)Eu_(0.1))O₂:Pr.

Shown in FIG. 8 is a system for implementation the fiber growth stepsdetailed above with respect to FIG. 7. System 128 includes a crucible132 or other container capable of housing the aforementioned startingmaterials and the dissolution of the starting materials into a precursorsolution 130. The crucible is then heated by a heater (not shown) todevelop a precursor gel within the crucible. A precursor fiber 134 isthen pulled or drawn from the gel and input into a drying oven 136. Theprecursor fiber 134 is pulled into the drying oven by pulling agent 138.The dried fiber 140 is then input by pulling agent 142 into a calciningand sintering oven 144. Upon sintering and annealing of fiber 140,pulling agents 146 remove the annealed fiber 148 from the sintering oven144. As discussed above, the annealed fiber or rod is then diced to forma plurality of scintillator fibers used to form a scintillator array.

The present invention also contemplates a plurality of single crystalfibers developed to form a scintillator array from a crystallizationsystem with garnet as the crystal phase. Each of the single crystalfibers operates as a scintillation element and is constructed to directlight out to a photodiode or other light detection element. Similar tothe ceramic fibers previously described, the single crystal fibers maybe aligned in parallel and bundled together to form a scintillator packor array similar to that shown in FIG. 6. Moreover, the single crystalfibers may have a uniform or common cross-sectional diameter whereuponthe resulting scintillator pack would be uniform. Alternately, thefibers of different cross-sectional diameters may be grown and combinedinto a single scintillator pack to maximize pack density and doseefficiency. In the embodiment illustrated in FIG. 6, each of the fibershas a circular cross-section; however, other cross-sectional shapes arecontemplated and within the scope of the invention.

Single crystal fiber is highly transparent and has very low impurity.This transparency improves the light collection efficiency of thecorresponding photodiode array. Moreover, because the crystallizationprocess is a purification process that can expel many undesirableimpurities, afterglow of each crystal fiber may be minimized. In oneembodiment, the single crystal fiber scintillator is composed of(Lu_(x)Tb_(1-x-y)Ce_(y))₃Al₅O₁₂ (LuTAG). “X” ranges from 0.5 to 1.5 and“y” ranges from 0.01 to 0.15. Due to the incongruent melting ofTb₃Al₅O₁₂, Lu is added to stabilize the garnet structure. Ce is added asthe scintillation activator. The garnet phase is essential fortransparent single crystal fibers. Further, operating at a congruentmelting composition is preferred for growing crack-resistant fibers.

Referring now to FIG. 9, a process map or steps of a technique fordeveloping a scintillator pack comprised of single crystal fibers isshown. The technique 150 begins at 152 with the mixing of raw materialsused as a base for scintillator crystal growth. In one embodiment, theraw materials include Tb₄O₇ (>99.99%), Lu₂O₃ (>99.99%), Al₂O₃ (>99.99%),and CeO₂ (>99.99%). The powder oxides are mixed by a ball mill withalcohol or distilled water and then dried at 152. The mixture is thenmelted at 154 in a molybdenum or iridium crucible at about 1800 to 1900°C. Stirring is used to homogenize the melt. Once the melt ishomogenized, a seed fiber is placed in the melt at 156. From the seedfiber, a single crystal rod or fiber is pulled at 158. The pulled fiberthen undergoes annealing at 160 at a prescribed temperature, i.e. 1500°C. Following annealing, the rod of single crystal scintillator materialis cut or diced at 162. The cutting at 162 parcels the single rod ofscintillator material into a number of single crystal fibers having acommon and uniform diameter. Preferably, each of the fibers will have acommon length.

The resulting fibers are then aligned in a mold at 164. The molddimensionally defines the scintillator pack to be formed from the singlecrystal fibers and also operates to closely pack the fibers. To increasethe number of fibers within the mold, some fibers of differentcross-sectional diameters may be used. As noted above, increasing thenumber of scintillation elements within a scintillator array increasesthe quantum detection efficiency (QDE) of the scintillator array. At166, the aligned fibers are cast with a reflective adhesive materialused to mechanically bond the fibers to one another into a singlestructure or assembly. The adhesive material mechanically bonds adjacentfibers to one another but may also be doped with a reflective materialsuch as TiO₂ to reduce cross-talk emissions between the scintillationelements. The bundle of cast fibers is then cured at 168 andsubsequently diced at 170 to form a number of scintillator packs 170.Preferably, the pack is sliced along lines perpendicular to the fibers”longitudinal axis. A layer of optically reflective material, such asreflector tape, is then coated on one surface of each scintillator arrayat 172. The surface may also be polished and the sputter coated withreflective material such as aluminum, silver, gold, and the like.Following application of the optically reflective layer, if any, anumber of uniformly sized scintillator arrays or packs result and theprocess ends at 174. If the fibers' were grown to be uniform in size andshape, then the array of each of the resulting packs will also beuniform in size shape.

Referring now to FIGS. 10 and 11, a number of methods are contemplatedto pull the crystal fiber from the melt. One method is pulling up,similar to the well-known Czochralski method 176 illustrated in FIG. 10.Another method is a pulling down method such as that shown in FIG. 11.For the pulling up method or technique of FIG. 10, the startingmaterials 178 are mixed in a crucible 180. A seed fiber is placed in thecrucible and is used for crystal growth. The seed fiber has a knowncrystal orientation (normally {111} direction). From the seed fiber, acrystal rod or fiber 182 is pulled using pulling agents 184. The pulledfiber 186 may then be processed (i.e. heated, sintered, annealed, andthe like) in accordance with the Czochralski method.

For the pulling down method 188 schematically shown in FIG. 11, thestarting materials 190 are placed in a crucible 192 having an orificemachined at the bottom thereof. The orifice has a diameter of about 0.2to 0.8 mm depending on the desired fiber diameter. The pulling rate isabout 1-10 mim/minutes. A seed fiber is used to start the crystalgrowth. The seed fiber has a known crystal orientation (normally {111}direction). The crucible 192 is first heated to about 50 to 100° C.above the melting temperature of the composition, then the temperatureis decreased to about 20° C. above the melting temperature andmaintained at that level. The seed fiber is then inserted into the meltslowly. When a small part of the seed (normally a few mm are in themelt), the pulling starts. The crystal growth 194 is pulled by agents196 under Argon atmosphere to prevent the oxidation of the crucible 192.The resultant fiber 198 is then cut into a certain length and annealedin a controlled atmosphere [normally Argon with certain oxygen (O₂)partial pressure]. The annealing temperature is around 1500° C.

Referring now to FIG. 12 package/baggage inspection system 200 includesa rotatable gantry 202 having an opening 204 therein through whichpackages or pieces of baggage 216 may pass. The rotatable gantry 202houses a high frequency electromagnetic energy source 206 as well as adetector assembly 208 having scintillator arrays comprised ofscintillator cells similar to that shown in FIG. 6. A conveyor system210 is also provided and includes a conveyor belt 212 supported bystructure 214 to automatically and continuously pass packages or baggagepieces through opening to be scanned. Objects are fed through opening byconveyor belt 212, imaging data is then acquired, and the conveyor belt212 removes the packages 216 from opening 204 in a controlled andcontinuous manner. As a result, postal inspectors, baggage handlers, andother security personnel may non-invasively inspect the contents ofpackages 216 for explosives, knives, guns, contraband, etc.

Therefore, in accordance with one embodiment of the present invention, aCT detector array includes a plurality of collimator elements configuredto collimate x-rays projected thereat as well as a non-pixelatedscintillator pack formed of a material that illuminates upon receptionof x-rays. The CT detector array further includes a photodiode arrayoptically coupled to the non-pixelated scintillator pack and configuredto detect illumination from the scintillator pack and output electricalsignals responsive thereto.

In accordance with another embodiment of the present invention, a CTdetector array comprising a non-pixelated array of scintillationelements configured to illuminate upon the reception of high frequencyelectromagnetic energy and coupled to an array of light detectionelements configured to detect illumination of the array of scintillationelements and output a plurality of electrical signals generallyindicative of high frequency electromagnetic energy received by thearray of scintillation elements is provided. The detector array isformed by developing the plurality of single crystal fibers ofscintillation material and casting the plurality of crystal fibers withan adhesive material. The detector array is further formed by curing theplurality of crystal fibers in adhesive material to form a cured packand cuffing the cured pack to a specified dimension.

According to another embodiment of the present invention, a method ofmanufacturing a CT detector array having a non-pixelated scintillatorarray includes the steps of developing a material base from whichscintillators may be grown and pulling a rod of scintillating materialfrom a material base. The method further includes cuffing the rod toform a plurality of scintillator fibers and aligning the plurality ofscintillator fibers into a scintillator bundle. The scintillator bundleis then sliced into a number of scintillator packs whereupon a reflectorcoating is applied to the number of scintillator packs.

The present invention has been described in terms of the preferredembodiment, and it is recognized that equivalents, alternatives, andmodifications, aside from those expressly stated, are possible andwithin the scope of the appending claims.

1. A method of manufacturing a CT detector array having a non-pixelatedscintillator array, the method comprising the steps of: developing amaterial base from which scintillators may be grown; pulling a rod ofscintillator material from the material base; cutting the rod to form aplurality of scintillator fibers; aligning the plurality of scintillatorfibers into a scintillator bundle; slicing the scintillator bundle intoa number of scintillator packs; and applying a reflector coating to thenumber of scintillator packs.
 2. The method of claim 1 wherein the stepof developing a material base includes the steps of: dissolving a numberof chemicals to form a precursor solution; and heating the precursorsolution to form a transparent gel.
 3. The method of claim 2 furthercomprising the steps of: heating the pulled rod of scintillatormaterial; calcining the rod; sintering the rod; and annealing thesintered rod.
 4. The method of claim 3 further comprising the step ofconverting the rod into a ceramic phase having a garnet structure priorto the sintering step.
 5. The method of claim 3 wherein the step ofdeveloping a material base includes the steps of: mixing a number ofpowder oxides with a ball mill and a dissolving solution; drying thedissolved solution; melting the dissolved solution; and homogenizing thedissolved solution.
 6. The method of claim 5 wherein the number ofpowder oxides includes Tb₄O₇, Lu₂O₃, Al₂O₃, and Ce₂O₃ and the dissolvingsolution includes alcohol.
 7. The method of claim 5 wherein the step ofpulling includes the steps of: growing a seed fiber in the homogenizedsolution; and pulling the seed fiber downward to develop the rod ofscintillator material.
 8. The method of claim 5 further comprising thestep of optically coupling the scintillator packs to a photodiode arrayconfigured to detect illumination from the scintillator pack and outputelectrical signals responsive thereto, the photodiode array having aplurality of photodiodes.
 9. The method of claim 8 wherein the couplingfurther comprises aligning each photodiode with a single respectivescintillator pack to detect light from the scintillator fibers therein.10. The method of claim 2 wherein the number of chemicals includeslutetium acetate hydrate, terbium acetate hydrate, cerium nitrate, andaluminum formate hydrate.
 11. The method of claim 2 wherein the numberof chemicals includes Y₂O₃, Gd₂ O₃, Eu₂ O₃, and Pr(NO₃)₃×H₂O.
 12. Amethod for constructing a non-pixelated scintillator array comprisingthe steps of: developing a plurality of single crystal fibers ofscintillation material; casting the plurality of single crystal fiberswith an adhesive material; curing the plurality of single crystal fibersand adhesive material to form a cured pack of a first dimension; cuttingthe cured pack to a specified dimension that is different from the firstdimension; and wherein the plurality of crystal fibers has a uniformcross-sectional diameter.
 13. The method of claim 12 wherein the step ofdeveloping further includes the step of growing the plurality of singlecrystal fibers from a mixture of Tb₄O₇, Lu₂O₃, Al₂O₃ and CeO₂.
 14. Themethod of claim 13 wherein the step of growing further comprises:incorporating one of distilled water and alcohol into the mixture;allowing the mixture to dry; and melting and homogenizing the driedmixture.
 15. The method of claim 14 further comprising the step ofpulling crystal fibers from the homogenized mixture.
 16. The method ofclaim 12 further comprising the step of coating a layer of reflectivematerial to one end surface of the cured pack.
 17. The method of claim12 further comprising the step of sputter coating reflective metal onone end surface of the cured pack.
 18. The method of claim 12 furthercomprising the step of depositing adhesive material in any voidsexisting between adjacent crystal fibers.
 19. A method of manufacturinga CT detector array comprising the steps of: preparing a material basefrom which scintillators may be grown; pulling a rod of scintillatormaterial from the material base; cutting the rod to form a plurality ofscintillator fibers; aligning the plurality of scintillator fibers intoa scintillator bundle; slicing the scintillator bundle into a number ofscintillator packs; applying a reflector coating to the number ofscintillator packs; optically coupling one of the scintillator packs toa single light detection element configured to detect illumination ofthe scintillator pack and output electrical signals generally indicativeof high frequency electromagnetic energy received by the scintillatorpack.
 20. The method of claim 19 further comprising the steps of:heating the pulled rod of scintillator material; calcining the rod;sintering the rod; and annealing the sintered rod.